The overall objective of this research will be to determine the mechanisms which operate to control gene transcription in aging animals. The concentration of each DNA-dependent RNA polymerase in nuclei and mitochondria of liver, heart, lung, and brain of C57BL/6J mice will be determined throughout its life span. The enzymes will be measured after resolution by DEAE-Sephadex chromatography. The level of each polymerase will be correlated with the measured rates of RNA synthesis in the tissues. The mitochondrial DNA of these tissues will be examined by isopycnic centrifugation for an age dependent accumulation of single strand cleavages. A search will also be conducted for factors required for specific initiation and termination of RNA synthesis.